1. Field of the Invention
The present invention relates to efficient matting agents based on precipitated silicas, their preparation, and their use in inks and paints.
2. Description of the Background
Precipitated silicas have been used for a long time as matting agents in paints. The matting properties of these compounds derive from a disperse reflection of light at the paint surface roughened by silica particles. The efficiency of matting agents is therefore determined by the reflection value at different observation angles (generally 60° and 85°) and also the initial mass required for sufficient matting. The surfaces thus treated ought to have a matt, satin gloss, but without any rough effect. The roughness of a surface can be determined, for example, by way of the average roughness value Ra and the depth of roughness Rz. The requirements imposed on matting agents, the necessary measurement methods, and also general information can be found, for example, in Degussa AG's pigment brochure series, No. 21 (2002).
The matting of a paint surface is naturally also dependent on the amount of matting agent used. Since precipitated silicas in addition to their matting effect also cause an increase in the viscosity of the paint, there are limits to the extent to which it is possible to increase the silica fraction in a paint.
The object was therefore to find silicas which at the same mass fraction as the known silicas possess an improved matting effect.